Pipe breakage control valve device

ABSTRACT

An input/output port  1  of a hose rupture control valve unit  100  is attached to a bottom port of a hydraulic cylinder  102 , and an input/output port  2  is connected to one of actuator ports of a control valve  103  via an actuator line  105 . The valve unit comprises a poppet valve body  5  serving as a main valve, a first spool valve body  6  serving as a pilot valve operated with a pilot pressure supplied as an external signal and having a pilot variable throttle portion  6   a  to operate the poppet valve body  5 , a second spool valve body  50  operated with a pilot pressure and having a sub-variable throttle portion  50   a  to control a sub-flow rate, and a small relief valve  7  having the function of an overload relief valve.

TECHNICAL FIELD

The present invention relates to a hose rupture control valve unit (hoserupture valve), which is provided in a hydraulic machine, such as ahydraulic excavator, for preventing a drop of a load upon rupture of acylinder hose.

BACKGROUND ART

In a hydraulic machine, e.g., a hydraulic excavator, there is a need forpreventing a drop of a load even if a hose or steel pipe for supplying ahydraulic fluid to a hydraulic cylinder, serving as an actuator fordriving the load, e.g., an arm, should be ruptured. To meet such a need,a hose rupture control valve unit, also called a hose rupture valve, isprovided in the hydraulic machine. FIG. 14 is a hydraulic circuitdiagram showing a typical conventional hose rupture control valve unit,and FIG. 15 is a sectional view of the hose rupture control valve unit.

Referring to FIGS. 14 and 15, a hose rupture control valve unit 200comprises a housing 204 provided with two input/output ports 201, 202and a reservoir port 203. The input/output port 201 is directly attachedto a bottom port of a hydraulic cylinder 102, the input/output port 202is connected to one of actuator ports of a control valve 103 via ahydraulic hose 105, and the reservoir port 203 is connected to areservoir 109 via a drain hose 205. Within the housing 204, there areprovided a main spool 211 operated with a pilot pressure supplied as anexternal signal from a manual pilot valve 108, a check valve 212 forfluid supply, a poppet valve body 214 controlled by a pilot portion 213which is provided on the main spool 211, and an overload relief valve215 for releasing an abnormal pressure.

In the conventional hose rupture control valve unit 200 having theabove-described construction, a hydraulic fluid is supplied to thebottom side of the hydraulic cylinder 102 by supplying the hydraulicfluid from the control valve 103 to the bottom side through thefluid-supply check valve 212 in the valve unit 200. Also, the hydraulicfluid is discharged from the bottom side of the hydraulic cylinder 102by operating the main spool 211 of the valve unit 200 with the pilotpressure, as an external signal, so as to first open the poppet valvebody 214 controlled by the pilot portion 213 which is provided on themain spool 211, and to then open a variable throttle portion 211 a alsoprovided on the main spool 211, thereby draining the hydraulic fluid tothe reservoir 109 while controlling a flow rate of the hydraulic fluid.

The poppet valve body 214 is provided in series with the main spool 211,and has the function (load check function) of reducing the amount ofleakage in a condition of holding the load pressure on the bottom sideof the hydraulic cylinder 102.

The overload relief valve 215 functions to drain the hydraulic fluid andprevent hose rupture in case that an excessive external force acts uponthe hydraulic cylinder 102 and the hydraulic pressure supplied to thebottom side of the hydraulic cylinder 102 is brought into ahigh-pressure level.

Also, if the hydraulic hose 105 leading from the control valve 103 tothe input/output port 202 should be ruptured, the check valve 212 andthe poppet valve body 214 are closed to prevent a drop of a loadsupported by the hydraulic cylinder 102. In such an event, by operatingthe main spool 211 with the pilot pressure from the manual pilot valve108 and adjusting an opening area of the variable throttle portion 211a, it is possible to slowly contract the hydraulic cylinder 102 underaction of the weight of the load itself and to move the load to a safetyposition.

Numerals 107 a and 107 b denote main relief valves for limiting amaximum pressure in the circuit.

Further, JP, A 3-249411 discloses a hose rupture control valve unitutilizing a proportional seat valve to reduce an overall size of thevalve unit. FIG. 16 shows the disclosed hose rupture control unit.

Referring to FIG. 16, a hose rupture control valve unit 300 comprises ahousing 323 provided with an input port 320, a work port 321 and areservoir port 322. The input port 320 is connected to one of actuatorports of a control valve 103, the work port 321 is connected to a bottomport of a hydraulic cylinder 102, and the reservoir port 322 isconnected to a reservoir 109 via a drain hose 205. Within the housing323, there are provided a check valve 324 for fluid supply, aproportional seat valve 325, an overload relief valve 326, and a pilotvalve 340. The pilot valve 340 is operated with a pilot pressuresupplied as an external signal from a manual pilot valve 108 (see FIG.14), and the proportional seat valve 325 is operated with the operationof the pilot valve 340. The overload relief valve 326 is incorporated inthe proportional seat valve 325.

A hydraulic fluid to the bottom side of the hydraulic cylinder 102 issupplied by supplying the hydraulic fluid from the control valve 103 tothe bottom side through the fluid-supply check valve 324 in the valveunit 300. Also, the hydraulic fluid is discharged from the bottom sideof the hydraulic cylinder 102 by operating the pilot valve 340 of thevalve unit 300 with the pilot pressure, as an external signal, to openthe proportional seat valve 325, thereby draining the hydraulic fluid tothe reservoir 109 while controlling a flow rate of the hydraulic fluid.The proportional seat valve 325 has the function (load check function)of reducing the amount of leakage in a condition of holding the loadpressure on the bottom side of the hydraulic cylinder 102.

The overload relief valve 326 functions to open the proportional seatvalve 325 for draining the hydraulic fluid and preventing hose rupturein case that an excessive external force acts on the hydraulic cylinder102 and the hydraulic pressure supplied to the bottom side of thehydraulic cylinder 102 is brought into a high-pressure level.

Also, if a hydraulic hose 105 leading from the control valve 103 to theinput port 320 should be ruptured, the check valve 324 and theproportional seat valve 325 are closed to prevent a drop of a loadsupported by the hydraulic cylinder 102. In such an event, by operatinga spool 341 of the pilot valve 340 with the pilot pressure and adjustingan opening area of the proportional seat valve 325, it is possible toslowly contract the hydraulic cylinder 102 under action of the weight ofthe load itself and to move the load to a safety position.

DISCLOSURE OF THE INVENTION

However, the above-described prior arts have a problem that it isdifficult to reduce a pressure loss and to cut down an overall size andproduction cost of the valve unit.

More specifically, in the prior art shown in FIGS. 14 and 15, variouscomponents, i.e., the check valve 212 for fluid supply, the main spool211, the poppet valve body 214 controlled by the pilot portion 213provided on the main spool 211, and the overload relief valve 215, areseparately provided corresponding to the respective functions.Therefore, incorporating all those components in the housing 204 of acertain restricted size imposes a limitation on sizes of the individualcomponents. Also, there has been a difficulty in reducing the productioncost.

On the other hand, since all of the hydraulic fluid discharged from thehydraulic cylinder 102 passes through the main spool 211, a spool valvebody of the main spool 211 is required to have a larger diameter.Further, because of the main spool 211 and the poppet valve body 214being provided in series, the hydraulic fluid passes through these twovalve elements at a large flow rate. Accordingly, when those parts areincorporated in the housing 204 of the certain restricted size, theirsizes are necessarily limited, which may result in that a sufficientflow passage is not ensured and a pressure loss is increased. Inaddition, a pressure loss is also inevitably produced with such aconstruction that the hydraulic fluid passes at a large flow ratethrough both of the main spool 211 and the poppet valve body 214provided in series.

The hose rupture control valve unit is mounted on the bottom side of aboom cylinder or the rod side of an arm cylinder. A boom and an arm, towhich the boom cylinder and the arm cylinder are attached, are each aworking member operated to rotate in the vertical direction. If the sizeof the housing 204 is selected to a relatively large value inconsideration of the problem of a pressure loss, this selection wouldincrease a risk that the hose rupture control valve unit may be damagedupon hitting against rocks or any other obstacles during the operationof the boom or the arm. It has been thus difficult to design the hoserupture control valve unit appropriately.

In the prior art disclosed in JP, A 3-249411, shown in FIG. 16, theoverload relief valve 326 is incorporated in the proportional seat valve325, which is controlled by the pilot valve 340, so that theproportional seat valve 325 has not only the function of the main spool211, but also the functions of the poppet valve body 214 and theoverload relief valve 215 in the above-described former prior art.Therefore, the number of components is reduced as compared with thatneeded in the above-described former prior art, and a reduction in sizeof the valve unit can be achieved to some extent while lessening apressure loss. With this disclosed prior art, however, the check valve324 for fluid supply is still an essential component. In other words,there is a demand for a further improvement in reducing the size and theproduction cost of the valve unit.

To overcome the problems mentioned above, the applicant proposed thefollowing invention in JP, A 10-110776 (filing data: Apr. 21, 1998;corresponding to U.S. Appl. No. 09/294,431, EP Appl. No. 99201251.8,Korean Appl. No. 1999-13956, and Chinese Appl. No. 99105093.2).

“A hose rupture control valve unit provided between a supply/drain portof a hydraulic cylinder and a hydraulic hose for controlling a flow rateof a hydraulic fluid coming out from the supply/drain port to thehydraulic hose in accordance with an external signal, wherein the valveunit comprises a poppet valve body serving as a main valve slidablydisposed in a housing provided with a cylinder connecting chamberconnected to the supply/drain port, a hose connecting chamber connectedto the hydraulic hose, and a back pressure chamber, the poppet valvebody being able to selectively cut off and establish communicationbetween the cylinder connecting chamber and the hose connecting chamber,and changing an opening area depending on the shift amount thereof, anda spool valve body serving as a pilot valve disposed in a pilot passageconnecting the back pressure chamber and the hose connecting chamber,and operated in accordance with the external signal to cut off andcontrol a rate of pilot flow passing through the pilot passage dependingon the shift amount thereof, the poppet valve body being provided with afeedback variable throttle passage which has an initial opening areawhen the poppet valve body is in a cutoff position, and increases anopening area thereof depending on the shift amount of the poppet valvebody, thereby controlling the rate of pilot flow coming out from thecylinder connecting chamber to the back pressure”.

With the thus-constructed valve unit of the earlier filed invention, inoperation of supplying the hydraulic fluid to the bottom side of thehydraulic cylinder, since the feedback variable throttle passage has theinitial opening area, the poppet valve body is opened when a pressure inthe hose connecting chamber rises to a level higher than a loadpressure, allowing the hydraulic fluid to be supplied to the bottom sideof the hydraulic cylinder (conventional check valve function on thesupply side).

In operation of discharging the hydraulic fluid from the bottom side ofthe hydraulic cylinder, when the spool valve body is operated inaccordance with the external signal and the pilot flow is produced at arate depending on the shift amount of the spool valve body, the poppetvalve body is opened and the shift amount thereof is controlleddepending on the pilot flow rate. Therefore, most of the hydraulic fluidon the bottom side of the hydraulic cylinder passes through the poppetvalve body, whereas the remaining hydraulic fluid passes through thefeedback variable throttle passage, the back pressure chamber and thespool valve body. Both the flows of the hydraulic fluid are then drainedto the reservoir (conventional main spool function).

Further, in operation of holding the load pressure on the bottom side ofthe hydraulic cylinder, the poppet valve body is in the cutoff positionand holds the load pressure, thereby reducing the amount of leakage(load check function).

Thus, the valve unit of the earlier filed invention can fulfill theleast necessary functions of a hose rupture control valve unit (i.e.,the check valve function on the supply side, the main spool function,and the load check function). Also, in the valve unit of the earlierfiled invention, the poppet valve body is only one component arranged ina flow passage through which the hydraulic fluid passes at a large flowrate. It is hence possible to reduce a pressure loss, and to cut down anoverall size and production cost of the valve unit.

An object of the present invention is to improve the earlier filedinvention and to provide a hose rupture control valve unit which canreduce a pressure loss and cut down an overall size and production costof the valve unit while ensuring various functions that are the leastnecessary as a hose rupture control valve unit, and which can offersmooth flow control characteristics and set a more variety of flowcontrol characteristics.

(1) To achieve the above object, the present invention provides a hoserupture control valve unit provided between a supply/drain port of ahydraulic cylinder and a hydraulic hose for controlling a flow rate of ahydraulic fluid coming out from the supply/drain port to the hydraulichose in accordance with an external signal, wherein the valve unitcomprises a poppet valve body serving as a main valve slidably disposedin a housing provided with a cylinder connecting chamber connected tothe supply/drain port, a hose connecting chamber connected to thehydraulic hose, and a back pressure chamber, the poppet valve body beingable to selectively cut off and establish communication between thecylinder connecting chamber and the hose connecting chamber, andchanging an opening area depending on the shift amount thereof; afeedback variable throttle passage provided in the poppet valve body,having an initial opening area when the poppet valve body is in a cutoffposition, and increasing an opening area thereof depending on the shiftamount of the poppet valve body; a first variable throttle portiondisposed in a pilot passage connecting the back pressure chamber and thehose connecting chamber, and operated in accordance with the externalsignal to cut off and control a rate of pilot flow flowing from thecylinder connecting chamber to the hose connecting chamber through thefeedback variable throttle passage, the back pressure chamber and thepilot passage; and a second variable throttle portion disposed in asub-passage connecting the cylinder connecting chamber and the hoseconnecting chamber, and operated in accordance with the external signalto cut off and control a rate of sub-flow passing through thesub-passage.

The construction that the poppet valve body and the first variablethrottle portion are provided and the poppet valve body includes thefeedback variable throttle passage having an initial opening area, isthe same as that of the earlier filed invention. With this construction,a pressure loss can be reduced and an overall size and production costof the valve unit can be cut down, while ensuring various functions thatare the least necessary as a hose rupture control valve unit.

Further, the second variable throttle portion is provided in thesub-passage so that it is given with the function of flow rate controlin the fine operating range. Therefore, flow rate control in the fineoperation range performed by the second variable throttle portion andcontrol of the poppet valve body performed by the first variablethrottle portion can made separately from each other. As a result,smooth flow control characteristics are obtained and a more variety offlow control characteristics can be set.

(2) In the above (1), preferably, opening timings of the first andsecond variable throttle portions are set such that the second variablethrottle portion is opened earlier than the first variable throttleportion in accordance with the external signal.

With this feature, as mentioned in the above (1), the second variablethrottle portion is given with the function of flow rate control in thefine operating range, and flow rate control in the fine operation rangeperformed by the second variable throttle portion and control of thepoppet valve body performed by the first variable throttle portion canmade separately from each other.

(3) In the above (1), preferably, the first variable throttle portionand the second variable throttle portion are provided on separate spoolvalve bodies.

With this feature, the opening timings of the first variable throttleportion and the second variable throttle portion can be changed by notonly the notch position of each of variable throttle portion, but alsothe strength of a spring acting upon each spool valve body. Therefore,flow control characteristics can be set with good accuracy.

(4) In the above (1), preferably, the first variable throttle portionand the second variable throttle portion are provided on the same spoolvalve body.

With this feature, the number of parts of the valve unit is reduced andthe size of the valve unit can be further reduced.

(5) In any of the above (1) to (4), preferably, the hose rupture controlvalve unit further comprises means for cutting off the sub-passage afteropening the poppet valve.

In the construction wherein the sub-passage and the second variablethrottle portion are provided in addition to the pilot passage and thefirst variable throttle portion as set forth in the above (1), the pilotflow rate and the sub-flow rate join with each other on the side of thehose connecting chamber. Therefore, the flow rate increases in a joiningarea and the downstream side thereof, which increases a passage pressureloss and causes a jet stream in the joining area to such an extent thatthe pressure in the back pressure chamber is increased or fluctuated.This results in a possibility that the poppet valve body may not beopened to have an opening area as per instructed by an external signaland control of a main flow rate may be adversely affected.

By cutting off the sub-passage after opening of the poppet valve body,only the pilot flow passes through the joining area after thesub-passage has been cut off. It is therefore possible to suppress anincrease of the passage pressure loss and the occurrence of a jet streamdue to joining of the pilot flow rate and the sub-flow rate, and toreduce an influence upon the control of the main flow rate.

(6) In the above (5), preferably, the means for cutting off thesub-passage is a land portion provided on a spool valve body includingthe second variable throttle portion, the land portion cutting off aflow passage of the second variable throttle portion when the spoolvalve body is shifted a predetermined distance or more.

With this feature, since the land portion is just additionally formed onthe spool valve body, the sub-passage can be cut off with a simpleconstruction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a hydraulic circuit diagram showing a hose rupture controlvalve unit according to a first embodiment of the present invention,along with a hydraulic drive system in which the valve unit is disposed.

FIG. 2 is a sectional view showing the structure of a portion, i.e., apoppet valve body and a first spool valve body, of the hose rupturecontrol valve unit shown in FIG. 1

FIG. 3 is a sectional view showing the structure of another portion,i.e., a small relief valve, of the hose rupture control valve unit shownin FIG. 1.

FIG. 4 is a graph showing the relationships of an opening area of thepoppet valve body and an opening area of a feedback slit with respect tothe shift amount (stroke) of the poppet valve body.

FIG. 5 is a graph showing the relationships of a characteristic of flowrate passing through a pilot variable throttle portion (pilot flowrate), a characteristic of flow rate passing through the poppet valvebody (main flow rate), a characteristic of flow rate passing through asub-variable throttle portion (sub-flow rate), and a characteristic oftotal flow rate with respect to a pilot pressure in the hose rupturecontrol valve unit shown in FIG. 1.

FIG. 6 is a hydraulic circuit diagram showing, as a comparative example,a hose rupture control valve unit of the earlier filed invention, alongwith a hydraulic drive system in which the valve unit is disposed.

FIG. 7 is a graph showing the relationships of a flow rate passingthrough a pilot variable throttle portion of a spool valve body (pilotflow rate) and a flow rate passing through a poppet valve body (mainflow rate) with respect to a pilot pressure in the hose rupture controlvalve unit shown in FIG. 6.

FIG. 8 is a hydraulic circuit diagram showing a hose rupture controlvalve unit according to a second embodiment of the present invention,along with a hydraulic drive system in which the valve unit is disposed.

FIG. 9 is a sectional view showing the structure of a portion, i.e., apoppet valve body and a spool valve body, of the hose rupture controlvalve unit shown in FIG. 8.

FIG. 10 is a hydraulic circuit diagram showing a hose rupture controlvalve unit according to a third embodiment of the present invention,along with a hydraulic drive system in which the valve unit is disposed.

FIG. 11 is a sectional view showing the structure of a portion, i.e., apoppet valve body and a spool valve body, of the hose rupture controlvalve unit shown in FIG. 10.

FIG. 12 is a graph showing the relationships of a characteristic of flowrate passing through a pilot variable throttle portion (pilot flowrate), a characteristic of flow rate passing through the poppet valvebody (main flow rate), a characteristic of flow rate passing through asub-variable throttle portion (sub-flow rate), and a characteristic oftotal flow rate with respect to a pilot pressure in the hose rupturecontrol valve unit shown in FIG. 10.

FIG. 13 is a sectional view of principal part of a hose rupture controlvalve unit according to a fourth embodiment of the present invention.

FIG. 14 is a hydraulic circuit diagram showing a conventional hoserupture control valve unit, along with a hydraulic drive system in whichthe valve unit is disposed.

FIG. 15 is a sectional view showing the structure of a portion, i.e., apoppet valve body and a spool valve body, of the hose rupture controlvalve unit shown in FIG. 14.

FIG. 16 illustrates an opening area of the poppet valve body and anopening area of a feedback slit with respect to the shift amount(stroke) of the poppet valve body in the conventional hose rupturecontrol valve unit.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will be described belowwith reference to the drawings.

FIG. 1 is a hydraulic circuit diagram showing a hose rupture controlvalve unit according to a first embodiment of the present invention, andFIGS. 2 and 3 are sectional views each showing the structure of the hoserupture control valve unit.

Referring to FIG. 1, numeral 100 denotes a hose rupture control valveunit of this embodiment. A hydraulic drive system, in which the valveunit 100 is disposed, comprises a hydraulic pump 101; a hydraulicactuator (hydraulic cylinder) 102 driven by a hydraulic fluid deliveredfrom the hydraulic pump 101; a control valve 103 for controlling a flowof the hydraulic fluid supplied from the hydraulic pump 101 to thehydraulic cylinder 102; main overload relief valves 107 a, 107 bconnected to actuator lines 105, 106, which are hydraulic hoses extendedfrom the control valve 103, for limiting a maximum pressure in thehydraulic circuit; a manual pilot valve 108, and a reservoir 109.

As shown in FIGS. 1 and 2, the hose rupture control valve unit 100comprises a housing 3 provided with two input/output ports 1 and 2. Theinput/output port 1 is directly attached to a bottom-side supply/drainport 102 a of the hydraulic cylinder 102, and the input/output port 2 isconnected to one 103 a of actuator ports 103 a, 103 b of the controlvalve 103 via the actuator line 105. The actuator port 103 b isconnected to a rod-side supply/drain port 102 b of the hydrauliccylinder 102 via the actuator line 106.

Within the housing 3, there are provided a poppet valve body 5 servingas a main valve; a first spool valve body 6 serving as a pilot valvewhich is operated with a pilot pressure supplied as an external signalfrom the manual pilot valve 108, thereby operating the poppet valve body5; a second spool valve body 50 operated with the same pilot pressure asthat supplied to the first spool valve body 6 and controlling a smallrange of flow rate; and a small relief valve 7 having the function of anoverload relief valve.

Also, within the housing 3, there are defined a cylinder connectingchamber 8 connected to the input/output port 1, a hose connectingchamber 9 connected to the input/output port 2, and a back pressurechamber 10. The poppet valve body 5 serving as a main valve is slidablydisposed in the housing 3 such that it is subjected at it back surfaceto a pressure in the back pressure chamber 10, and it selectively cutsoff and establishes communication between the cylinder connectingchamber 8 and the hose connecting chamber 9 while its opening area ischanged depending on the shift amount of thereof. The poppet valve body5 is provided with a feedback slit 11 serving as a feedback variablethrottle passage which increases its opening area depending on the shiftamount of the poppet valve body 5 and controls a rate of pilot flowcoming out from the cylinder connecting chamber 8 to the back pressurechamber 10 depending on the opening area thereof. The back pressurechamber 10 is closed by a plug 12 (see FIG. 2), and a spring 13 isdisposed in the back pressure chamber 10 for holding the poppet valvebody 5 in the cutoff position as shown.

Further, in the housing 3, pilot passages 15 a, 15 b are formed tocommunicate the back pressure chamber 10 and the hose connecting chamber9 with each other, and the first spool valve body 6 serving as a pilotvalve is disposed between the pilot passages 15 a and 15 b. The pilot 15b comprises two parts, i.e., passage portions 15 b 1, 15 b 2. Thepassage portion 15 b 2 serves also as part of a sub-passage (describedlater).

The first spool valve body 6 has a pilot variable throttle portion 6 acomprising a plurality of notches and being able to communicate thepilot passages 15 a, 15 b with each other. A spring 16 for setting aninitial valve-opening force of the pilot variable throttle portion 6 ais disposed at an operating end of the first spool valve body 6 in thevalve-closing direction, and a pressure bearing chamber 17, to which thepilot pressure is introduced as an external signal, is formed at anoperating end of the first spool valve body 6 in the valve-openingdirection. The shift amount of the first spool valve body 6 isdetermined by a control force given by the pilot pressure (externalsignal) introduced to the pressure bearing chamber 17 and an urgingforce produced by the spring 16. Depending on the shift amount of thefirst spool valve body 6, the opening area of the pilot variablethrottle portion 6 a is changed to selectively cut off and control thepilot flow rate passing through the pilot passages 15 a, 15 b. Thespring 16 is supported by a spring receiver 18 including a threadedportion 19 which enables an initial setting force of the spring 16(i.e., the initial valve-opening force of the pilot variable throttleportion 6 a) to be adjusted. A spring chamber 20, in which the spring 16is disposed, is connected to the reservoir via a drain passage 21 sothat the first spool valve body 6 moves smoothly.

Moreover, in the housing 3, sub-passages 15 c, 15 d are formed tocommunicate the cylinder connecting chamber 8 and the hose connectingchamber 9 with each other. The second spool valve body 50 is disposedbetween the sub-passages 15 c and 15 d. The sub-passage 15 d isconnected to the hose connecting chamber 9 via the portion 15 b 2 of thepilot passage 15 b. Thus, the passage portion 15 b 2 serves as not onlythe pilot passage, but also the sub-passage.

The second spool valve body 50 has a sub-variable throttle portion 50 acomprising a plurality of notches and being able to communicate thesub-passages 15 c, 15 d with each other. A spring 51 for setting aninitial valve-opening force of the sub-variable throttle portion 50 a isdisposed at an operating end of the second spool valve body 50 in thevalve-closing direction, and a pressure bearing chamber 52, to which thepilot pressure is introduced as an external signal, is formed at anoperating end of the second spool valve body 50 in the valve-openingdirection. The shift amount of the second spool valve body 50 isdetermined by a control force given by the pilot pressure (externalsignal) introduced to the pressure bearing chamber 52 and an urgingforce produced by the spring 51. Depending on the shift amount of thesecond spool valve body 50, the opening area of the sub-variablethrottle portion 50 a is changed to selectively cut off and control asub-flow rate passing through the sub-passages 15 c, 15 d. The spring 51is supported by a spring receiver 53 including a threaded portion 54which enables an initial setting force of the spring 51 (i.e., theinitial valve-opening force of the sub-variable throttle portion 50 a)to be adjusted. A spring chamber 55, in which the spring 51 is disposed,is connected to the reservoir via the drain passage 21 so that thesecond spool valve body 50 moves smoothly.

Additionally, in the housing 3, there are formed a relief passage 15 epositioned on the inlet side of the small relief valve 7, and a drainpassage 15 f positioned on the outlet side of the small relief valve 7.The relief passage 15 e is connected to the cylinder connecting chamber8, and the drain passage 15 f is connected to the reservoir via thedrain passage 21. Further, a throttle 34 as means for producing apressure is provided in the drain passage 15 f, and a signal passage 36is branched from a point between the small relief valve 7 and thethrottle 34.

At the operating end of the first spool valve body 6 in thevalve-opening direction, another pressure bearing chamber 35 is definedin addition to the pressure bearing chamber 17 to which the pilotpressure (external signal) introduced. The signal passage 36 isconnected to the pressure bearing chamber 35 so that the pressureproduced by the throttle 34 acts upon the first spool valve body 6 as adriving force on the same side as the pilot pressure introduced theretoas an external signal.

FIG. 3 shows the detailed construction of the pressure bearing chambers17, 35. The first spool valve body 6 is divided into a main spoolportion 6 b including the pilot variable throttle portion 6 a formedthereon, and a piston portion 6 c positioned on the side remote from thespring 16 in an adjacent relation to the main spool portion 6 b. Thepressure bearing chamber 17 is provided at an end of the piston portion6 c on the side remote from the main spool portion 6 b, and the pressurebearing chamber 35 is provided at a portion where the main spool portion6 b and the piston portion 6 c are adjacent to each other. Thisconstruction enables both of the pilot pressure introduced to thepressure bearing chamber 17 and the pressure produced by the throttle 34and introduced to the pressure bearing chamber 35 to act upon thevariable throttle portion 6 a in the opening direction.

FIG. 4 is a graph showing the relationships of an opening area of thepoppet valve body 5 and an opening area of the feedback slit 11 withrespect to the shift amount (stroke) of the poppet valve body 5. Whenthe poppet valve body 5 is in the cutoff position, the feedback slit 11has a predetermined initial opening area A₀. As the poppet valve body 5starts moving from the cutoff position and the shift amount thereofincreases, the opening areas of the poppet valve body 5 and the feedbackslit 11 are increased proportionally. Because of the feedback slit 11having the initial opening area A₀, the poppet valve body 5 can performthe function of the conventional check valve for fluid supply (describedlater).

FIG. 5 is a graph showing the relationships of a flow rate passingthrough the pilot variable throttle portion 6 a of the first spool valvebody 6 (pilot flow rate) and a flow rate passing through the poppetvalve body (main flow rate) with respect to the pilot pressure suppliedas an external signal from the manual pilot valve 108, the relationshipbetween those flow rates and a flow rate passing through thesub-variable throttle portion 50 a of the second spool valve body 50(sub-flow rate), as well as the relationship between those flow ratesand a total flow rate passing through the valve unit 100. X1 representsa characteristic line of flow rate control performed by the pilotvariable throttle portion 6 a, X2 represents a characteristic line offlow rate control performed by the poppet valve body 5, and X3represents a characteristic line of flow rate control performed by thesub-variable throttle portion 50 a. X4 represents a characteristic lineof total flow rate control, i.e., a characteristic line of flow ratecontrol performed by the valve unit 100.

In FIG. 5, the range of the pilot pressure from 0 to P₂ corresponds to adead zone of the pilot variable throttle portion 6 a of the first spoolvalve body 6. Even with the pilot pressure rising in that range, thefirst spool valve body 6 is held stopped by the initial setting force ofthe spring 16 or, even if shifted, it is located in an overlap regionresulting before the pilot variable throttle portion 6 a is opened. Thepilot variable throttle portion 6 a therefore remains in the cutoffposition. As indicated by the characteristic line X1, when the pilotpressure reaches P₂, the pilot variable throttle portion 6 a of thefirst spool valve body 6 starts opening and the opening area of thepilot variable throttle portion 6 a increases as the pilot pressurerises over P₂. Correspondingly, the rate of fluid flow passing throughthe pilot variable throttle portion 6 a, i.e., the pilot flow ratepassing through the pilot passages 15 a and 15 b, also increases.

Also, the range until the pilot flow rate reaches a predetermined valueat the pilot pressure P₃(>P₂) corresponds to a dead zone of the poppetvalve body 5. During this dead zone, a pressure fall occurred in theback pressure chamber 10 due to the presence of the feedback slit 11 isinsufficient even with the pilot flow rate produced to some extent, andtherefore the poppet valve body 5 is held in the cutoff position by theinitial setting force of the spring 13. As indicated by thecharacteristic line X2, when the pilot flow rate reaches a predeterminedvalue at the pilot pressure P₃, the poppet valve body 5 starts openingand the opening area of the poppet valve body 5 increases as the pilotpressure rises over P₃. Correspondingly, the rate of fluid flow passingthrough the poppet valve body 5, i.e., the main flow rate, alsoincreases.

Further, the range of the pilot pressure from 0 to P₁ corresponds to adead zone of the sub-variable throttle portion 50 a of the second spoolvalve body 50. Even with the pilot pressure rising in that range, thesecond spool valve body 50 is held stopped by the initial setting forceof the spring 51 or, even if shifted, it is located in an overlap regionresulting before the sub-variable throttle portion 50 a is opened. Thesub-variable throttle portion 50 a therefore remains in the cutoffposition. As indicated by the characteristic line X3, when the pilotpressure reaches P₁, the sub-variable throttle portion 50 a of thesecond spool valve body 50 starts opening and the opening area of thesub-variable throttle portion 50 a increases as the pilot pressure risesover P₁. Correspondingly, the rate of fluid flow passing through thesub-variable throttle portion 50 a, i.e., the sub-flow rate passingthrough the sub-passages 15 c and 15 d, also increases.

In addition, by satisfying P₁>P₂ and setting the opening timing suchthat the sub-variable throttle portion 50 a of the second spool valvebody 50 is opened with the pilot pressure at earlier timing than thepilot variable throttle portion 6 aof the first spool valve body 6, thesub-variable throttle portion 50 a is given with the function of flowrate control in the fine operation range.

As a result of that the respective flow rates passing through the pilotvariable throttle portion 6 a of the first spool valve body 6, thepoppet valve body 5, and the sub-variable throttle portion 50 a of thesecond spool valve body 50 are changed as described above, the totalflow rate passing through the valve unit 100 is changed as indicated bythe characteristic line X4.

In FIG. 5, a gradient of the characteristic line X1 relating to thepilot variable throttle portion 6 a of the first spool valve body 6 canbe adjusted by changing the notch size of the pilot variable throttleportion 6 a, and a start end of the characteristic line X1, i.e., theopening timing of the pilot variable throttle portion 6 a, can beadjusted by adjusting the strength (initial setting force) of the spring16 or the notch position of the pilot variable throttle portion 6 a.Also, by so changing the gradient or opening timing of thecharacteristic line X1 of the pilot variable throttle portion 6 a of thefirst spool valve body 6, the pilot pressure at which the pilot pressurereaches the predetermined value is changed, thus enabling the openingtiming of the poppet valve body 5 (start end of the characteristic lineX2) to be adjusted. Further, a gradient of the characteristic line X3relating to the sub-variable throttle portion 50 a of the second spoolvalve body 50 can be adjusted by changing the notch size of thesub-variable throttle portion 50 a, and a start end of thecharacteristic line X3, i.e., the opening timing of the sub-variablethrottle portion 50 a, can be adjusted by adjusting the strength(initial setting force) of the spring 51 or the notch position of thesub-variable throttle portion 50 a.

Next, the operation of the hose rupture control valve unit 100 thusconstructed will be described.

A description is first made of the operation in a normal condition wherethe actuator line 105 is not ruptured.

1) Supply of Hydraulic Fluid to Bottom Side of Hydraulic Cylinder 102

When a control lever of the manual pilot valve 108 is operated in thedirection A denoted in FIG. 1 to shift the control valve 103 to take aright-hand position as viewed in the drawing, the hydraulic fluid fromthe hydraulic pump 101 is supplied to the hose connecting chamber 9 ofthe valve unit 100 through the control valve 103, causing the pressurein the hose connecting chamber 9 to rise. At this time, since thepressure in the cylinder connecting chamber 8 of the valve unit 100 isequal to the load pressure on the bottom side of the hydraulic cylinder102 and the feedback slit 11 has the initial opening area A₀, thepressure in the back pressure chamber 10 is also equal to that loadpressure. Accordingly, while the pressure in the hose connecting chamber9 is lower than the load pressure, the poppet valve body 5 is held inthe cutoff position. As soon as the pressure in the hose connectingchamber 9 becomes higher than the load pressure, the poppet valve body 5starts to move upward in the drawing, allowing the hydraulic fluid toflow into the cylinder connecting chamber 8. Thus, the hydraulic fluidfrom the hydraulic pump 101 is supplied to the bottom side of thehydraulic cylinder 102. While the poppet valve body 5 is moving upward,the hydraulic fluid in the back pressure chamber 10 displaces into thecylinder connecting chamber 8 through the feedback slit 11 for ensuringsmooth opening of the poppet valve body 5. The hydraulic fluid from therod side of the hydraulic cylinder 102 is drained to the reservoir 109through the control valve 103.

2) Discharge of Hydraulic Fluid from Bottom Side of Hydraulic Cylinder102 to Control Valve 103

When the control lever of the manual pilot valve 108 is operated in thedirection B denoted in FIG. 1 to shift the control valve 103 to take aleft-hand position as viewed in the drawing, the hydraulic fluid fromthe hydraulic pump 101 is supplied to the rod side of the hydrauliccylinder 102 through the control valve 103. At the same time, the pilotpressure from the manual pilot valve 108 is introduced to the pressurebearing chamber 17 of the first spool valve body 6 to shift the firstspool valve body 6 with the pilot pressure, whereupon the pilot variablethrottle portion 6 aof the first spool valve body 6 has an opening areacorresponding the shift amount thereof. Accordingly, as described above,the hydraulic fluid passes through the pilot passages 15 a, 15 b at thepilot flow rate depending on the pilot pressure, and the poppet valvebody 5 is opened and controlled in the shift amount thereof depending onthe pilot flow rate. The pilot pressure from the manual pilot valve 108is also introduced to the pressure bearing chamber 2 of the second spoolvalve body 50 to shift the second spool valve body 50 with the pilotpressure, whereupon the pilot variable throttle portion 50 a of thesecond spool valve body 50 has an opening area corresponding the shiftamount thereof. Accordingly, as described above, the hydraulic fluidpasses through the sub-passages 15 c, 15 d at the sub-flow ratedepending on the pilot pressure. As a result, the hydraulic fluid on thebottom side of the hydraulic cylinder 102 is drained to the controlvalve 103 and then to the reservoir 109 while being controlled by thepoppet valve body 5, the first spool valve body 6, and the second spoolvalve body 50 of the valve unit 100.

3) Holding of Load Pressure on Bottom Side of Hydraulic Cylinder 102

In a condition where the load pressure on the bottom side of thehydraulic cylinder 102 becomes high, as occurred in the case of holdinga lifted load with the control valve 103 maintained at the neutralposition, the poppet valve body 5 in the cutoff position performs thefunction of holding the load pressure and reducing the amount of leakage(load check function) as with the conventional load check valve.

4) In Case of Excessive External Force Acting upon Hydraulic Cylinder102

In case that an excessive external force acts upon the hydrauliccylinder 102 and the pressure in the cylinder connecting chamber 8becomes high, the pressure in the relief passage 15 e rises and thesmall relief valve 7 is opened, allowing the hydraulic fluid to flowinto the drain passage 15 f in which the throttle 34 is disposed. As aresult, the pressure in the signal passage 36 rises and the first spoolvalve body 6 is shifted to open the pilot variable throttle portion 6 afor producing a pilot flow passing through the pilot passages 15 a, 15b. Hence, the poppet valve body 5 is also opened and the hydraulic fluidbrought into a high-pressure level under action of the external force isdrained to the reservoir 109 through the overload relief valve 107 aconnected to the actuator line 105, thereby preventing damage of theequipment. On that occasion, since the hydraulic fluid passes the smallrelief valve 7 at a small flow rate, the function equivalent to that ofthe conventional overload relief valve can be realized with the smallrelief valve 7 having a small size.

If the actuator line 105 should be ruptured, the poppet valve body 5 inthe cutoff position functions as a load check valve (holding valve)similarly to the above-described case of holding a lifted load, therebyblocking outflow of the hydraulic fluid on the bottom side of thehydraulic cylinder 102 to prevent a drop of a boom. When lowering theboom down to a safety position from that condition, an operator operatesthe control lever of the manual pilot valve 108 in the direction Bdenoted in FIG. 1. With this lever operation, as described above, thepilot pressure from the manual pilot valve 108 is introduced to thepressure bearing chamber 17 of the spool valve body 6 to open the spoolvalve body 6 with the pilot pressure, whereupon the poppet valve body 5is also opened. Accordingly, the hydraulic fluid on the bottom side ofthe hydraulic cylinder 102 can be discharged under flow rate control andthe boom can be slowly lowered.

With this embodiment, as described above, just by providing the poppetvalve body 5 in a flow passage through which all of the hydraulic fluidsupplied to and discharged from the hydraulic cylinder 102 passes, thepoppet valve body 5 can fulfill the functions of the check valve forfluid supply, the load check valve, and the overload relief valve in theconventional hose rupture control valve unit. Therefore, a valve unithaving a small pressure loss can be constructed, and highly efficientoperation can be achieved with a less energy loss. Also, since the valveunit 100 has a smaller size than the conventional hose rupture controlvalve unit, a possibility that the valve unit may be damaged duringworks is reduced, and flexibility in design is increased. Furthermore,the reduced number of components contributes to reducing the failurefrequency, improving the reliability, and enabling the valve unit to beproduced at a relatively low cost.

Moreover, the poppet valve body 5 is opened by causing the hydraulicfluid, that is brought into a high-pressure level under action of anexcessive external force, to act upon the small relief valve 7, and thehydraulic fluid passes through the small relief valve 7 at a small flowrate when the high-pressure hydraulic fluid is released to the reservoirthrough the main overload relief valve 107 a. The function equivalent tothat of the conventional overload relief valve can be therefore realizedwith the small relief valve 7 having a small size. In addition, sincethe hydraulic fluid is released from the small relief valve 7 to thereservoir via the drain passage 21 that is identical to a drain lineformed in the conventional valve unit, a drain hose specific to theoverload relief valve is no longer required in the valve unit 100, androuting of the hose around the valve unit 100 can be simplified.

The above-described advantages are the same as those obtained by JP, A10-110776, i.e., the invention earlier filed by the applicant.

In the valve unit 100 of the present invention, the sub-passages 15 c,15 d and the second spool valve body 50 are provided in addition to theconstruction of the valve unit of the earlier filed invention, so thatsmooth flow control characteristics can be obtained and a more varietyof flow control characteristics can be set. These features will bedescribed below in more detail with reference to the drawings.

FIG. 6 shows, as a comparative example, the valve unit of the earlierfiled invention, and a description is first made of this valve unit. InFIG. 6, identical members to those in FIG. 1 are denoted by the samenumerals.

Referring to FIG. 6, numeral 200 denotes the valve unit of the earlierfiled invention. The valve unit 200 is the same as the one 100 of thisembodiment shown in FIG. 1 except for that neither the sub-passages 15c, 15 d nor the second spool valve body 50, shown in FIG. 1, areprovided in a housing 203, and the relief passage 15 e is connected tonot the cylinder connecting chamber 8, but the back pressure chamber 10.

To describe such a difference in position to which the relief passage 15e is connected, a similar overload relief function can also be obtainedby connecting the relief passage 15 e to not the cylinder connectingchamber 8, but the back pressure chamber 10, because the high pressurein the hydraulic cylinder 102 is transmitted to the relief passage 15 ethrough the feedback slit 11 and the back pressure chamber 10. In thiscase, however, since the feedback slit 11 (throttle) is interposedbetween the hydraulic cylinder 102 and the relief passage 15 e, there isa possibility that the operation of the small relief valve 7 may beunstable in dynamic fashion. By contrast, in the valve unit 100 of thisembodiment shown in FIG. 1, since the high pressure in the hydrauliccylinder 102 is directly introduced to the relief passage 15 e, it ispossible to operate the small relief valve 7 with a better response andto ensure a stable relief function.

FIG. 7 is a graph showing the relationships of the flow rate passingthrough a pilot variable throttle portion 6 a of the spool valve body 6(pilot flow rate) and a flow rate passing through a poppet valve body 5(main flow rate) with respect to the pilot pressure supplied as anexternal signal in the valve unit 200 shown in FIG. 6, as well as therelationship between those flow rates and a total flow rate passingthrough the valve unit 200. Y1 represents a characteristic line of flowrate control performed by the pilot variable throttle portion 6 a, Y2represents a characteristic line of flow rate control performed by thepoppet valve body 5, and Y3 represents a characteristic line of totalflow rate control, i.e., a characteristic line of flow rate controlperformed by the valve unit 200.

In FIG. 7, the range of the pilot pressure from 0 to P₁₁ corresponds toa dead zone of the pilot variable throttle portion 6 a of the spoolvalve body 6. Even with the pilot pressure rising in that range, thespool valve body 6 is held stopped by the initial setting force of thespring 16 or, even if shifted, it is located in an overlap regionresulting before t he pilot variable throttle portion 6 a is opened. Thepilot variable throttle portion 6 a therefore remains in the cutoffposition. As indicated by the characteristic line Y1, when the pilotpressure reaches P₁₁, the pilot variable throttle portion 6 a of thespool valve body 6 starts opening and the opening area of the pilotvariable throttle portion 6 a increases as the pilot pressure rises overP₁₂. Correspondingly, the rate of fluid flow passing through the pilotvariable throttle portion 6 a, i.e., the pilot flow rate passing throughpilot passages 15 a and 15 b, also increases.

Also, the range until the pilot flow rate reaches a predetermined valueat the pilot pressure P₁₂ (>P₁₁) corresponds to a dead zone of thepoppet valve body 5. During this dead zone, a pressure fall occurred inthe back pressure chamber 10 due to the presence of the feedback slit 11is insufficient even with the pilot flow rate produced to some extent,and therefore the poppet valve body 5 is held in the cutoff position bythe initial setting force of the spring 13. As indicated by thecharacteristic line Y2, when the pilot flow rate reaches a predeterminedvalue at the pilot pressure P₁₂, the poppet valve body 5 starts openingand the opening area of the poppet valve body 5 increases as the pilotpressure rises over P₁₂. Correspondingly, the rate of fluid flow passingthrough the poppet valve body 5, i.e., the main flow rate, alsoincreases.

As a result of that the respective flow rates passing through the pilotvariable throttle portion 6 a of the spool valve body 6 and the poppetvalve body 5 are changed as described above, the total flow rate passingthrough the valve unit 200 is changed as indicated by the characteristicline Y3.

In the valve unit 200 of the earlier filed invention, however, sinceflow rate control in the fine operation range (range where the amount bywhich a lever of the manual control valve 108 is operated is small andthe pilot pressure is low) and control of the poppet valve body 5 areboth performed by the same pilot variable throttle portion 6 a of thespool valve body 6, the overall range of the flow rate control ischanged upon change of flow control characteristics in the fineoperation range and smooth flow control characteristics are not obtainedsometimes.

For example, if the flow control characteristic of the pilot variablethrottle portion 6 a of the spool valve body 6 is modified in the valveunit 200 of the earlier filed invention by changing the characteristicline from Y1 to Y4 having a smaller gradient in order to improveoperability in the fine operation range (fine operability), the openingtiming of the poppet valve body 5 is shifted from the point P₁₂ to P₁₃and the characteristic line of the flow rate control performed by thepoppet valve body 5 is changed from Y2 to Y5, whereby the characteristicof the total flow rate passing through the valve unit 200 is changed asindicated by Y6. In this case, the fine operability is improved becauseof the characteristic line Y4 having a smaller gradient, but a maximumflow rate (flow rate resulting under a maximum pilot pressure when thelever is fully operated) passing through the valve unit 200 is reduced.Therefore, the overall range of the flow rate control is reduced andsmooth flow control characteristics are not obtained. Also, when theopening timing of the spool valve body 6 is shifted from the point P₁₁,the opening timing of the poppet valve body 5 is likewise shifted fromthe point P₁₂, thus resulting in that the overall range of the flow ratecontrol is reduced and smooth flow control characteristics are notobtained.

By contrast, in the valve unit 100 of this embodiment shown in FIG. 1,the second spool valve body 50 is further provided and the sub-variablethrottle portion 50 a of the second spool valve body 50 is disposed inthe sub-passages 15 c, 15 d separate from the pilot passages 15 a, 15 bof the poppet valve body 5. Therefore, even when the flow controlcharacteristic of the sub-variable throttle portion 50 a is changed, thepilot flow rate passing through the pilot passages 15 a, 15 b is notchanged and the opening timing of the poppet valve body 5 is also notchanged. Also, by setting the opening timing such that the sub-variablethrottle portion 50 a is opened with rising of the pilot pressure atearlier timing than the pilot variable throttle portion 6 aof the firstspool valve body 6, the sub-variable throttle portion 50 a is given withthe function of flow rate control in the fine operation range. Statedotherwise, in this embodiment, the flow rate control in the fineoperation range and the control performed by the poppet valve body 5 areseparated from each other by adding the sub-variable throttle portion 50a of the second spool valve body 50.

By thus separating the flow rate control in the fine operation range andthe control performed by the poppet valve body 5, the opening timing ofthe poppet valve body 5 can be set regardless of the flow rate controlin the fine operation range, and the overall range of the flow ratecontrol is not changed even when the flow control characteristic in thefine operation range is changed. Hence, even when modifying thecharacteristic line of the flow rate control to have a smaller gradientfor improving the operability in the fine operation range, smooth flowcontrol characteristics can be obtained.

Assuming, for example, that the characteristic line of the sub-variablethrottle portion 50 a of the second spool valve body 50 is given by abroken line X5 in FIG. 5, even when the characteristic line is modifiedto have a smaller gradient, i.e., to X3 used in this embodiment, theopening timing of the poppet valve body 5 is not changed from the pointP₃, whereas the characteristic of the total flow rate passing throughthe valve unit 100 is changed from X6 to X4. In other words, the flowcontrol characteristic in the fine operation range is changed, butchange of the maximum flow rate passing through the valve unit 100 isslight and the overall range of the flow rate control is hardly changed.Likewise, when the opening timing of the sub-variable throttle portion50 a of the second spool valve body 50 is shifted from the point P₁, theopening timing of the poppet valve body 5 is not changed from the pointP₃, thus resulting in that the overall range of the flow rate control ishardly changed.

Furthermore, when characteristics (gradient of the characteristic line Xand the opening timing) of the pilot variable throttle portion 50 a ofthe second spool valve body 50 are changed to modify the flow controlcharacteristic of the poppet valve body 5 on the contrary to the abovecase, the flow control characteristic in the fine operation rangeprovided by the sub-variable throttle portion 50 a of the second spoolvalve body 50 is hardly changed.

As described hereinabove, since the flow control characteristic in thefine operation range and the flow control characteristic of the poppetvalve body 5 can be set individually and the overall range of the flowrate control is hardly changed even with change of the flow controlcharacteristic in the fine operation range, smooth flow controlcharacteristics can be achieved even in the case of modifying thecharacteristic line of the flow rate control to have a smaller gradientfor improving the operability in the fine operation range.

Also, a more variety of flow control characteristics can be set byoptionally combining change in characteristics of the sub-variablethrottle portion 50 a of the second spool valve body 50 and change incharacteristics of the pilot variable throttle portion 6 a of the firstspool valve body 6 (change in characteristics of the poppet valve body5) with each other. Therefore, flexibility in design is increased andthe valve unit can be applied to various actuators (hydraulic cylinders)having different demanded flow control characteristics.

Further, in this embodiment, since the pilot variable throttle portion 6a and the sub-variable throttle portion 50 a are provided on the spoolvalve bodies 6, 50 separate from each other, the opening timings of thepilot variable throttle portion 6 a and the sub-variable throttleportion 50 a can be changed by not only the notch position, but also thestrengths of the springs 16, 51 acting upon the first and second spoolvalve bodies 6, 50.

A second embodiment of the present invention will be described withreference to FIGS. 8 and 9. In these drawings, identical members tothose in FIGS. 1 and 2 are denoted by the same numerals.

Referring to FIGS. 8 and 9, numeral 100A denotes a hose rupture valveunit of this embodiment. Within a housing 3A of the valve unit 100A,there is disposed a single spool valve body 60 that is operated with thepilot pressure supplied from the manual pilot valve 108 as an externalsignal. This spool valve body 60 serves as both of the first spool valvebody 6 and the second spool valve body 50 in the first embodiment.

More specifically, the spool valve body 60 is divided into a pistonsection 6 c and a main spool section 6 d. The main spool section 6 dincludes a pilot variable throttle portion 6 a comprising a plurality ofnotches and being able to communicate the pilot passage 15 a and apilot/sub-passage 15 h with each other, and a sub-variable throttleportion 50 a comprising a plurality of notches and being able tocommunicate the sub-passage 15 c and the pilot/sub-passage 15 h witheach other. A common outlet port 58, to which the pilot/sub-passage 15 his connected, is provided between the pilot variable throttle portion 6a and the sub-variable throttle portion 50 a. Further, a spring 16A forsetting an initial valve-opening force of the pilot variable throttleportion 6 a and the sub-variable throttle portion 50 a is disposed at anoperating end of the main spool section 6 d in the valve-closingdirection, and a pressure bearing chamber 17, to which the pilotpressure is introduced as an external signal, is formed at an operatingend of the piston section 6 c in the valve-opening direction._@The shiftamount of the spool valve body 60 is determined by a control force givenby the pilot pressure (external signal) introduced to the pressurebearing chamber 17 and an urging force produced by the spring 16A.Depending on the shift amount of the spool valve body 60, the openingarea of each of the pilot variable throttle portion 6 a and thesub-variable throttle portion 50 a is changed to selectively cut off andcontrol a pilot flow rate passing through the pilot passage 15 a and thepilot/sub-passage 15 h and a sub-flow rate passing through thesub-passage 15 c and the pilot/sub-passage 15 h. In addition, a pressurebearing chamber 35 is formed in an area where the main spool section 6 dand the piston section 6 c are adjacent to each other. When the smallrelief valve 7 is operated, the pressure produced by the throttle 34 isintroduced to the pressure bearing chamber 35 and then contributes tothe overload relief function.

In this embodiment, flow control characteristics of the pilot variablethrottle portion 6 a, the poppet valve body 5 and the sub-variablethrottle portion 50 a are the same as those in the first embodimentshown in FIG. 5. Specifically, the sub-variable throttle portion 50 a isgiven with the function of flow rate control in the fine operation rangeby setting the opening timing such that the sub-variable throttleportion 50 a is opened at earlier timing than the pilot variablethrottle portion 6 a.

The other construction of the valve unit 100A is essentially the same asthat of the valve unit 100 of the first embodiment.

This embodiment having the above-described construction can also providethe advantages as follows. The opening timing of the poppet valve body 5can be adjusted regardless of the flow rate control in the fineoperation range by adjusting the notch size of each of the pilotvariable throttle portion 6 aand the sub-variable throttle portion 5 a,the notch position thereof, and the strength of the spring 16A.Therefore, the flow control characteristic in the fine operation rangeand the flow control characteristic of the poppet valve body 5 can beset individually and the overall range of the flow rate control ishardly changed even with change of the flow control characteristic inthe fine operation range. As a result, smooth flow controlcharacteristics can be achieved even when the characteristic line of theflow rate control is modified to have a smaller gradient for improvingthe operability in the fine operation range. Also, since a more varietyof flow control characteristics can be set, flexibility in design isincreased and the valve unit can be applied to various actuators(hydraulic cylinders) having different demanded flow controlcharacteristics.

Further, in this embodiment, since the pilot variable throttle portion 6a and the sub-variable throttle portion 50 a are provided on the samespool valve body 60, an additional advantage is obtained in that thenumber of parts and the size of the valve unit are reduced as comparedwith those in the first embodiment.

A third embodiment of the present invention will be described withreference to FIGS. 10 to 12. In these drawings, identical members tothose in FIGS. 1, 2, 8 and 9 are denoted by the same numerals.

Referring to FIGS. 10 and 11, numeral 100B denotes a hose rupture valveunit of this embodiment. Within a housing 3A of the valve unit 10B,there is disposed a single spool valve body 60B that is operated withthe pilot pressure supplied from the manual pilot valve 108 as anexternal signal. As with the spool valve body 60, this spool valve body60B also serves as both of the first spool valve body 6 and the secondspool valve body 50 in the first embodiment.

More specifically, the spool valve body 60B in this embodiment isdivided into a piston section 6 c and a main spool section 6 e. The mainspool section 6 e includes a pilot variable throttle portion 6 acomprising a plurality of notches and being able to communicate thepilot passage 15 a and the pilot/sub-passage 15 h with each other, and asub-variable throttle portion 50 a comprising a plurality of notches andbeing able to communicate the sub-passage 15 c and the pilot/sub-passage15 h with each other. Further, the main spool section 6 e includes aland portion 61 provided on the outlet side of the sub-variable throttleportion 50 a. The land portion 61 functions as a means for cutting offthe sub-passage. When the main spool section 6 e is in the inoperativeposition (neutral position) as shown, the land portion 61 is positionedin an outlet port 58 to which the pilot/sub-passage 15 h is connected.When the main spool section 6 e is shifted a predetermined distance inthe valve-opening direction (downward as viewed in the drawing) with thepilot pressure supplied as an external signal, the land portion 61 fitsinto a spool bore of the housing 3A, thereby closing a flow passage ofthe sub-variable throttle portion 50 a on the side of the outlet port58. Herein, the predetermined distance necessary for the land 61 toclose the flow passage of the sub-variable throttle portion 50 a means astroke distance of the main spool section 6 e after the main spoolsection 6 e has shifted to open the pilot variable throttle portion 6 aand hence to open the poppet valve body 5.

FIG. 12 shows the relationships of a characteristic (X1) of flow ratepassing through the pilot variable throttle portion 6 a (pilot flowrate), a characteristic (X2) of flow rate passing through the poppetvalve body 5 (main flow rate), a characteristic (X3B) of flow ratepassing through the sub-variable throttle portion (sub-flow rate), and acharacteristic (X4) of total flow rate with respect to the pilotpressure supplied as an external signal.

In FIG. 12, when the pilot pressure reaches P₁, the sub-variablethrottle portion 50 a starts opening and the opening area of thesub-variable throttle portion 50 a increases as the pilot pressure risesover P₁. Correspondingly, the rate of fluid flow passing through thesub-variable throttle portion 50 a, i.e., the sub-flow rate passingthrough the sub-passage 15 c and the pilot/sub-passage 15 h, alsoincreases.

When the pilot pressure reaches P₂₁, the pilot variable throttle portion6 a now starts opening and the opening area of the pilot variablethrottle portion 6 a increases as the pilot pressure rises over P₂.Correspondingly, the rate of fluid flow passing through the pilotvariable throttle portion 6 a, i.e., the pilot flow rate passing throughthe pilot passage 15 a and the pilot/sub-passage 15 h, also increase.

When the pilot pressure further rises and reaches P₃, the poppet valvebody 5 starts opening and the opening area of the poppet valve body 5increases as the pilot pressure rises over P₃. Correspondingly, the rateof fluid flow passing through the poppet valve body 5, i.e., the mainflow rate, also increases.

Characteristics of the pilot flow rate and the main flow rate are thesame as those in the first and second embodiments. In this thirdembodiment, the land portion 51 is provided on the outlet side of thesub-variable throttle portion 50 a of the spool valve body 60B, and whenthe pilot pressure reaches a level near P₃, the land portion 61 startsclosing the flow passage of the sub-variable throttle portion 50 a onthe side of the outlet port 58. Then, the land portion 61 reduces theopening area of that flow passage as the pilot pressure rises over P₃,and completely cuts off that flow passage when the pilot pressurereaches P₄. Therefore, the rate of fluid flow passing through thesub-variable throttle portion 50 a, i.e., the sub-flow rate, startsreducing when the pilot pressure reaches a level near P₃, then decreasesas the pilot pressure rises over P₃, and finally becomes 0 when thepilot pressure reaches P₄.

With this embodiment having the above-described construction, since thepilot variable throttle portion 6 a and the sub-variable throttleportion 50 a are provided on the same spool valve body 60B, a similaradvantage as that in the second embodiment is obtained.

Further, this embodiment provides the following advantage because theland portion 51 functioning as a means for cutting off the sub-passageis provided on the spool valve body 60B.

In the construction wherein the sub-passages and the sub-variablethrottle portion 50 a are provided in addition to the pilot passages andthe pilot variable throttle portion 6 a as with the first and secondembodiments, the pilot flow rate and the sub-flow rate join with eachother on the side of the hose connecting chamber, e.g., in the passage15 b 2 in the first embodiment and at the outlet port 58 in the secondembodiment. Therefore, the flow rate increases in a joining area and thedownstream side thereof, and a pressure loss generated in the subsequentflow passage increases correspondingly. Also, in the joining area of thepilot flow rate and the sub-flow rate, a jet stream occurs due tocollision of two flows. Such an increase of the passage pressure lossand a jet stream occurred in the joining area increases or fluctuatesthe pressure in the back pressure chamber 10, thus resulting in apossibility that the poppet valve body 5 may not be opened to have anopening area as per instructed by an external signal and the control ofthe main flow rate may be adversely affected.

In this embodiment, since the sub-passage is cut off by the land portion61 after opening of the poppet valve body 5 as described above, only thepilot flow passes through the joining area after the sub-passage hasbeen cut off. It is therefore possible to suppress an increase of thepassage pressure loss and the occurrence of a jet stream due to joiningof the pilot flow rate and the sub-flow rate, to reduce an influenceupon the control of the main flow rate, and to realize smooth control ofthe main flow rate. Also, because of a reduction in pressure loss, ajoining passage can be narrowed and the size of the valve unit can befurther reduced. Moreover, since the land 61 is just additionally formedon the spool valve body 60B (main main spool section 6 e), thesub-passage can be cut off with a simple construction.

The above-described third embodiment is constructed by modifying thesecond embodiment, in which the pilot variable throttle portion and thesub-variable throttle portion are provided on a single pilot valve body,such that a means for cutting off the flow passage of the sub-variablethrottle portion is provided on the single pilot valve body. However, asimilar modification can also be added to the first embodiment whereinthe pilot variable throttle portion and the sub-variable throttleportion are provided on separate pilot valve bodies. FIG. 13 is anenlarged view of a portion including a second spool valve body in thecase where such a modification is added to the first embodiment.

Referring to FIG. 13, a land portion 61C is provided on a second spoolvalve body 50C at a position locating on the inlet side of asub-variable throttle portion 50 a thereof and corresponding to an inletport 59 to which the sub-passage 15 c is connected. When the secondspool valve body 50C is in the inoperative position (neutral position)as shown, the land portion 61C is positioned in the inlet port 59. Whenthe second spool valve body 50C is shifted a predetermined distance inthe valve-opening direction (downward as viewed in the drawing) with thepilot pressure supplied as an external signal and the poppet valve body5 (see FIG. 1) is opened, the land portion 61C fits into a spool bore ofthe housing 3, thereby closing a flow passage of the sub-variablethrottle portion 50 a on the side of the inlet port 59.

This embodiment having the above-described construction can provide thefollowing advantages in addition to similar advantages as obtained inthe first embodiment. Since the sub-passage is cut off by the landportion 61C after opening of the poppet valve body, only the pilot flowpasses through a joining area after the sub-passage has been cut off. Itis therefore possible to suppress an increase of the passage pressureloss and the occurrence of a jet stream due to joining of the pilot flowrate and the sub-flow rate, to reduce an influence upon the control ofthe main flow rate, and to realize smooth control of the main flow rate.Also, because of a reduction in pressure loss, a joining passage(passage 15 b shown in FIG. 1) can be narrowed and the size of the valveunit can be further reduced.

Industrial Applicability

According to the present invention, in a hose rupture control valveunit, a pressure loss can be reduce and an overall size and productioncost of the valve unit can be cut down while ensuring various functionsthat are the least necessary as a hose rupture control valve unit. Also,just by providing the second variable throttle portion in thesub-passage, smooth flow control characteristics are obtained and a morevariety of flow control characteristics can be set. As a result,flexibility in design is increased and the valve unit can be applied tovarious actuators (hydraulic cylinders).

Furthermore, according to the present invention, by providing a meansfor cutting off the sub-passage, an effect upon the poppet shift amountdue to a pressure loss in the joining passage and a jet stream occurredin the joining area can be reduced. It is therefore possible to realizesmooth control of the main flow rate with good accuracy, to narrow thejoining passage, and to further reduce the size of the valve unit.

What is claimed is:
 1. A hose rupture control valve unit (100; 100A;100B) provided between a supply/drain port (102 a) of a hydrauliccylinder (102) and a hydraulic hose (105) for controlling a flow rate ofa hydraulic fluid coming out from said supply/drain port to saidhydraulic hose in accordance with an external signal, wherein said valveunit comprises: a poppet valve body (5) serving as a main valve slidablydisposed in a housing (3) provided with a cylinder connecting chamber(8) connected to said supply/drain port (102 a), a hose connectingchamber (9) connected to said hydraulic hose (105), and a back pressurechamber (10), said poppet valve body being able to selectively cut offand establish communication between said cylinder connecting chamber andsaid hose connecting chamber, and changing an opening area depending onthe shift amount thereof; a feedback variable throttle passage (11)provided in said poppet valve body, having an initial opening area whensaid poppet valve body is in a cutoff position, and increasing anopening area thereof depending on the shift amount of said poppet valvebody; a first variable throttle portion (6 a) disposed in a pilotpassage (15 a, 15 b; 15 a, 15 h) connecting said back pressure chamberand said hose connecting chamber, and operated in accordance with theexternal signal to cut off and control a rate of pilot flow flowing fromsaid cylinder connecting chamber to said hose connecting chamber throughsaid feedback variable throttle passage, said back pressure chamber andsaid pilot passage; and a second variable throttle portion (50 a)disposed in a sub-passage (15 c, 15 d; 15 c, 15 h) connecting saidcylinder connecting chamber and said hose connecting chamber, andoperated in accordance with the external signal to cut off and control arate of sub-flow passing through said sub-passage.
 2. A hose rupturecontrol valve unit according to claim 1, wherein opening timings of saidfirst and second variable throttle portions are set such that saidsecond variable throttle portion (50 a) is opened earlier than saidfirst variable throttle portion (6 a) in accordance with the externalsignal.
 3. A hose rupture control valve unit according to claim 1,wherein said first variable throttle portion (6 a) and said secondvariable throttle portion (50 a) are provided on separate spool valvebodies (6,50).
 4. A hose rupture control valve unit according to claim1, wherein said first variable throttle portion (6 a) and said secondvariable throttle portion (50 a) are provided on the same spool valvebody (60; 60B).
 5. A hose rupture control valve unit according to claim1, further comprising means (61) for cutting off said sub-passage (15 c,15 h) after opening said poppet valve (5).
 6. A hose rupture controlvalve unit according to claim 5, wherein said means (61) for cutting offsaid sub-passage (15 c, 15 h) is a land portion (61) provided on a spoolvalve body (60B, 6 e) including said second variable throttle portion(50 a), said land portion cutting off a flow passage of said secondvariable throttle portion (50 a) when said spool valve body is shifted apredetermined distance or more.